Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A head-up display for a motor vehicle, including an image generating
device, from which radiation beams of an image, linearly polarized by a
polarizer 4 arranged on the image generating device on the light exit
side, are guided via an imaging optical unit to a windscreen and are
directed from the windscreen in the direction of a driver of the motor
vehicle. A reflective linear polarizer is arranged in the beam path of
the radiation beam between the image generating device and the
windscreen, the polarization direction of which linear polarizer
corresponds to the polarization direction of the radiation beam emitted
by the image generating device, and which linear polarizer reflects
differently polarized light radiating on the beam path from the
windscreen to the image generating device.

Claims:

1.-7. (canceled)

8. A head-up display for a motor vehicle, comprising: an image generating
device, from which beams of an image are guided; a polarizer arranged on
a light-exit side on the image generating device configured to linearly
s-polarize the beams of the image; an imaging optical unit configured to
guide the linearly s-polarized beams of the image to a windscreen of the
motor vehicle, wherein the linearly s-polarized beams of the image are
directed from the windscreen in a direction of a driver of the motor
vehicle; a reflecting linear polarizer arranged between the image
generating device and the windscreen, a polarization direction of the
reflecting linear polarizer corresponds to a polarization direction of
the beams emitted by the image generating device and which reflects light
that travels along a beam path from the windscreen to the image
generating device that has a different polarization.

9. The head-up display as claimed in claim 8, wherein the reflecting
linear polarizer is arranged on a light-exit-side polarizer of the image
generating device.

10. The head-up display as claimed in claim 9, wherein the reflecting
linear polarizer and the light-exit-side polarizer of the image
generating device are a common film.

11. A head-up display for a motor vehicle, comprising: an image
generating device, from which beams of an image are guided, a polarizer
arranged on a light-exit side on the image generating device configured
to linearly polarized the beams; an imaging optical unit configured to
guide the beams to a windscreen, wherein the beams are directed from the
windscreen in a direction of a driver of the motor vehicle; a reflecting
linear polarizer arranged between the image generating device and the
windscreen, the polarization direction of which is orientated
perpendicular with respect to the polarization direction of the beams
emitted by the image generating device and which reflects this light and
which absorbs or transmits light that travels along a beam path from the
windscreen to the image generating device that has a different
polarization.

12. The head-up display as claimed in claim 11, wherein the reflecting
linear polarizer is a mirror.

13. The head-up display as claimed in claim 11, further comprising: a
housing in which the image generating device and the imaging optical unit
are arranged, wherein the housing has an opening that is closed by a
light-transmissive cover panel and through which the beams from the image
generating device reaches the windscreen, and wherein the reflecting
linear polarizer is arranged on or in the cover panel.

14. The head-up display as claimed in one claim 11, wherein the image
generating device is a liquid-crystal display, through which a light
source can shine and which, on a light-entry side, has a p-polarizing
polarizer.

15. The head-up display as claimed in claim 12, wherein the mirror is a
part of the imaging optical unit.

16. The head-up display as claimed in claim 8, further comprising: a
housing in which the image generating device and the imaging optical unit
are arranged, wherein the housing has an opening that is closed by a
light-transmissive cover panel and through which the beams from the image
generating device reaches the windscreen, and wherein the reflecting
linear polarizer is arranged on or in the cover panel.

17. The head-up display as claimed in one claim 16, wherein the image
generating device is a liquid-crystal display, through which a light
source can shine and which, on a light-entry side, has a p-polarizing
polarizer.

18. The head-up display as claimed in claim 8, further comprising an
aspherical mirror arranged between the image generating device and the
windscreen.

19. The head-up display as claimed in claim 11, further comprising an
aspherical mirror arranged between the image generating device and the
windscreen.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This is a U.S. national stage of application No. PCT/EP2011/073732,
filed on Dec. 22, 2011. Priority is claimed on German Application No. 10
2010 055 839.7, filed Dec. 23, 2010; and German Application No. 10 2011
014 145.6 filed 16 Mar. 2011 the contents of which are incorporated here
by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a head-up display for a motor vehicle,
having an image generating device, from which beams of an image are
guided, linearly polarized by a polarizer arranged on the light-exit side
on the image generating device, via an imaging optical unit to a
windscreen, and are directed from the windscreen in the direction of a
driver of the motor vehicle.

[0004] 2. Description of Prior Art

[0005] In such a head-up display, a representation of information is
projected by a projection system into the windscreen for the driver of
the motor vehicle.

[0006] The image is generated by the image generating device. Terminating
with respect to the observer, an absorbing polarizing film is situated on
the image generating device. The light from the image generating device
is linearly polarized by the polarizing film. This polarization is
perpendicular to the plane of the projection.

[0007] Due to the light paths and the reflection of the beam of the
projection image at the windscreen, it is possible that the sun shines
directly into the image generating device. Due to the focusing of the
imaging optical unit, a significant amount of heat is introduced into the
image generating device.

[0008] To reduce the heating, it is known to arrange a cold mirror, which
is transparent or absorbing in the infrared spectral range, in the beam
path of the beam between image generating device and windscreen.

[0009] Nevertheless, sufficient luminous power can still be incident on
the image generating device for the latter to be heated to temperatures
which impair the generated image.

SUMMARY OF THE INVENTION

[0010] An object of one embodiment of the invention is to provide a
head-up display of the type mentioned in the introduction, which
significantly reduces solar irradiation of the image generating device.

[0011] According to one embodiment of the invention a reflecting linear
polarizer is arranged in the beam path between the image generating
device and the windscreen, the polarization direction of which
corresponds to the polarization direction of the beam emitted by the
image generating device and which reflects light that travels along the
beam path from the windscreen to the image generating device and has a
different polarization.

[0012] Light that is irradiated from the sun through the windscreen into
the beam path between windscreen and image generating device having a
polarization direction that does not correspond to the polarization
direction of the reflecting polarizer is reflected by the reflecting
linear polarizer and cannot cause heating of the image generating device.

[0013] The reflecting polarizer can be arranged at any location in the
beam path between the image generating device and the windscreen.

[0014] In one advantageous configuration, the reflecting polarizer can be
arranged on the light-exit-side polarizer of the image generating device.

[0015] No separate installation of the reflecting polarizer is necessary
if the reflecting polarizer and the light-exit-side polarizer of the
image generating device are formed in a common film.

[0016] In another embodiment, a reflecting linear polarizer can be
arranged in the beam path of the beam between the image generating device
and the windscreen, the polarization direction of which is orientated
perpendicular to the polarization direction of the beam emitted by the
image generating device and which reflects this light and which absorbs
or transmits light that travels along the beam path from the windscreen
to the image generating device and has a different polarization.

[0017] The beam emanating from the image generating device is directed
onwards by the reflecting polarizer toward the windscreen and from there
in the direction of the driver. One portion of the sunlight traveling in
the beam path from the windscreen to the image generating device is
reflected by the reflecting polarizer, and only another portion is
transmitted, with the result that only the transmitted portion can reach
the image generating device and cause the heating of it.

[0018] The reflecting polarizer can be a mirror of the imaging optical
unit.

[0019] In order to protect against external influences, the image
generating device and the imaging optical unit can be arranged inside a
housing, which has an opening closed by a light-transmissive cover panel
and through which the beam from the image generating device reaches the
windscreen.

[0020] The reflecting polarizer can be arranged on or in the cover panel.

[0021] For the purpose of simplifying installation, no separate
installation of cover panel and reflecting polarizer is necessary.

[0022] This configuration also results in high transmission values and
thus in a head-up display having a great efficiency.

[0023] In principle, when arranging the reflecting polarizer on the image
generating device, a further s-polarizing polarizer on the light-exit
side on the image generating device is not necessary.

[0024] Due to the less optimum polarization effect of reflecting
polarizers, which would result in lower contrast of the representation if
they were arranged alone on the light-exit side on the image generating
device, both a pure linearly absorbing polarizer and a reflecting
polarizer are preferably arranged on the light-exit side on the image
generating device.

[0025] If the image generating device is a liquid-crystal display, through
which a light source can shine and which, on the light-entry side,
carries a polarizing polarizer, clearing of the liquid-crystal display,
as a result of which no image is represented any more, is avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] One exemplary embodiment of the invention is illustrated in the
drawing and will be explained in more detail below. In the figures:

[0027] FIG. 1 is a basic illustration of a head-up display; and

[0028] FIG. 2 is a cross-section through a liquid-crystal display of the
head-up display according to FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] A liquid-crystal display 1, the details of which are shown in FIG.
2, which is a TFT liquid-crystal display, has on its rear side a first
polarizer 2, through which the light from a light source 3 enters,
linearly polarized, the liquid-crystal display 1.

[0030] Arranged on the light-exit side is, on the liquid-crystal display
1, first a linear s-polarizing second polarizer 4 and, thereon, a
reflecting linear polarizer 5 having the same polarization as the second
polarizer 4.

[0032] This beam is guided in a beam path 6 using imaging optical unit 1,
having a mirror 7 and an aspherical mirror 8, and a transparent cover
panel 9 onto a windscreen 10 of a motor vehicle and then reflected to the
region of the eyes 11 of a driver of the motor vehicle.

[0033] The cover panel 9 closes a housing 12, which is located below the
windscreen 10 and in which the liquid-crystal display 1, the light source
3, the mirrors 7, 8 and the imaging optical unit 8 are arranged.

[0034] By tilting the windscreen 10, the beam is deflected at the
windscreen 10 by an angle of between 110° and 140°.

[0035] This means that this deflection angle corresponds to a Brewster
angle α' of approximately 60°.

[0036] If the radiation 13 from the sun 14 is incident on the windscreen
10 from the outside under an angle which is close to the Brewster angle
a, this sunlight is polarized in part by the windscreen 10.

[0037] Owing to the Brewster angle, the sunlight has, after the windscreen
10, a p-polarized portion that is greater than the s-polarized portion.
This p-polarized portion is kept away particularly well from the
liquid-crystal display 1 by the reflecting polarizer 5 and thus cannot
heat it (FIG. 2).

[0038] The p-polarized portion is approximately 70%, while the s-polarized
portion is only approximately 30%.

[0039] Since therefore only the 30% s-polarized portion of the sunlight
can reach the liquid-crystal display 1 counter to the beam path 6 and
cause heating of the liquid-crystal display 1, this heating is so low
that it does not impair the function of the liquid-crystal display 1.

[0040] Thus, while there have shown and described and pointed out
fundamental novel features of the invention as applied to a preferred
embodiment thereof, it will be understood that various omissions and
substitutions and changes in the form and details of the devices
illustrated, and in their operation, may be made by those skilled in the
art without departing from the spirit of the invention. For example, it
is expressly intended that all combinations of those elements and/or
method steps which perform substantially the same function in
substantially the same way to achieve the same results are within the
scope of the invention. Moreover, it should be recognized that structures
and/or elements and/or method steps shown and/or described in connection
with any disclosed form or embodiment of the invention may be
incorporated in any other disclosed or described or suggested form or
embodiment as a general matter of design choice. It is the intention,
therefore, to be limited only as indicated by the scope of the claims
appended hereto.